Personal mobile communication (PMC) devices such as smart phones and Internet tablet computers are becoming increasingly ubiquitous. One factor driving the popularity of these devices is their use in geolocation and navigation. Built-in Global Positioning System (GPS) apparatus capture signals from GPS satellites and calculate a PMC device coordinate position from the signals. Position accuracies within 15 to 30 feet may be achieved. GPS received signal strength and frequencies largely render the GPS system line-of-sight and suitable for outdoor use, however.
There is an unserved need for location positioning and distance estimation within buildings. Examples include finding a friend or associate at a conference or convention, keeping track of children while shopping, asset tracking, electromagnetic interference (EMI) avoidance, etc.
Institute of Electrical and Electronic Engineers (IEEE) 802.11v, an emerging revision to the 802.11 wireless networking standards, defines various wireless client management enhancements to the standard. (Additional information regarding the IEEE 802.11 standard may be found in ANSI/IEEE Std. 802.11, Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications (published 1999; reaffirmed June 2003.)
Feature sets defined by 802.11v include certain wireless client localization capabilities to support PMC handoffs between wireless access points (APs). Other features include forwarding station position coordinates, transmitted signal strengths, antenna gain values, and other data around the network. Thus, under 802.11v, participants in enterprise associations with a particular AP may become aware of detailed characteristics of other clients and/or APs within a wireless network. Associated stations may make time-of-flight (TOF) measurements to determine inter-station distance based upon the speed of the signal propagation.
Such characteristics may be useful in wireless mobile device localization schemes. In some cases, however, a wireless mobile device may need to determine its distance from an AP or from another mobile device to which it is not wirelessly associated. In these cases, TOF measurements to determine distance may not be possible